Leading article: How Iraq has cast its shadow over a disastrous week

A video message from Ayman al-Zawahri, broadcast with the Khan tape, left no room for doubt. The al-Qa'ida leader described the "blessed London battle" of 7 July as direct revenge for the UK's actions in Iraq. The Government's argument that there is no link between the two events - and that Britain would have been targeted anyway - is looking increasingly forlorn.

Kenneth Clarke, who announced his decision to run for the Tory leadership this week, also exposed the Government's disarray over Iraq. In his first campaign speech, he made clear his view that the invasion of Iraq had increased the terror threat to the UK. Should Mr Clarke become Tory leader, this theme is bound to resurface many times. As an opponent of the invasion, he has an ability to put pressure on Mr Blair in a way his rivals for the Tory leadership do not.

Even on the shores of the Gulf of Mexico, powerful reverberations from the debacle over Iraq are being felt. The aftermath of Hurricane Katrina - particularly in the deluged city of New Orleans - has exposed the lack of preparedness of the Bush administration in the face of natural disasters. A third of the Louisiana National Guard - who would have been at the forefront of the emergency relief work this week - are serving in Baghdad. What is more, the units that are out of the country are the best trained and equipped for such situations. This has not been lost on the citizens of New Orleans, who are watching their city being devastated while an inadequate relief effort takes place.

The debate will surely soon shift to the cost of rebuilding. It is estimated tens of billions of dollars will be required by New Orleans alone. This will concentrate public attention in America on the £100m being spent each day by the President in Iraq. Exactly where, Americans are starting to ask, do President Bush's priorities lie? Just as in Britain, the strains created by the ill-judged intervention in Iraq are setting the parameters of political debate across the Atlantic.

Meanwhile, Iraq appears to be edging closer to the abyss of civil war. The new constitution looks likely to be vetoed by disaffected Sunnis in the October referendum, which could strangle Iraqi democracy at birth. And the insurgency continues to terrorise the country. It was this climate of insecurity that sparked a stampede in Baghdad this week in which almost a thousand Shia pilgrims died. Yet, the 140,000 US troops stationed in Iraq - including those Louisiana guardsmen - are seemingly incapable of halting the bloodshed. If anything, their presence is attracting new recruits to the insurgent ranks.

This has been a week of disaster, both natural and man-made. And at the eye of the storm lies Iraq. We are reaping the whirlwind of the duplicitous and arrogant manner in which our leaders took us to war. And we now find ourselves tied to the consequences of the calamity we have created in that nation. It is no wonder we are finding it so hard - in Tony Blair's unfortunate phrase - to "move on" from Iraq.